This application claims the priority of German Patent Application No. 199 59 563.1, filed in Germany, Dec. 10, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an air-permeable transport belt for transporting a fiber strand to be pneumatically condensed over a suction slit of a condensing zone of a spinning machine.
For the pneumatic condensing of a fiber strand leaving a drafting unit of a spinning machine it is important that the fiber strand is transported in the condensing zone disposed on an air-permeable transport element and still in a twist-free state and having fibers lying essentially parallel to one another, and that in the condensing zone an air stream is generated which flows through the transporting element, which air stream, depending on its width and/or direction determines the degree of condensing and which positions the fibers transversely to the transport direction and thus bundles or condenses the fiber strand. In the case of a fiber strand condensed in this way, a spinning triangle does not occur when twist is being imparted, so that the thread produced is more even, more tear-resistant and less hairy.
A transport belt of the above mentioned type is described in connection with a condensing arrangement in German published patent application 198 46 268 (corresponding U.S. Pat. No. 6,108,873. The transport belt is, in this case, perforated and is designed as a mesh belt or a sieve foil or advantageously as a close-meshed woven belt, which is driven glidingly over a hollow profile which comprises the suction slit.
In the design of a woven belt it is advantageously possible to provide a plurality of openings in a very small space, so that a very homogenous air stream is generated. At the points of intersection between the warp threads and the weft threads, tiny open pores form in which the fibers can adhere. The trapped fibers can, in time, block the perforations and thus impair the condensing effect. In the case of the mesh belt or the sieve foil variations, the above mentioned disadvantage is avoided, but the distance between the holes is significantly larger than in the case of the woven belt, so that the air stream is less homogenous.
It is an object of the present invention to produce a transport belt of the above mentioned type, in which the risk of a reduction in air-permeability with increasing operating time is avoided to a great extent, and in which an entirely homogenous air stream is possible at the same time.
This object has been achieved in accordance with the present invention in that the normally smooth transport belt has, at least in its effective area of the suction slit, a porous area.
The phrase xe2x80x9cporous areaxe2x80x9d can be taken not to mean a relatively coarse perforation, which occurs by stamping or as is the case with woven belts, but rather it is a porosity which is present in, for example, air-permeable plastic bags.
In order to produce a transport belt in accordance with the present invention, various production methods are possible:
A fine-grained, almost dust-like synthetic granulate can be sintered, whereby the granulate, just below its melting temperature, is pressed under pressure into a mould. Air can then pass through the baked granulate grains.
Alternatively, various kinds of granulate can be sintered together, for example granulates of polyamide and polystyrene, whereby a graining of approximately 50 xcexcm is ideal. The polystyrene part is subsequently dissolved by using a solvent, so that in this case also, a free airflow through the transport belt occurs.
Granulate blends with different melting points can also be melted together, whereby a synthetic with a higher melting temperature and a plastic with a lower melting temperature are mixed together in a fine-grain granulate, for example a polyamide with a polycarbonate. Injection into the mould takes place at a temperature which lies between the two melting points. The granulate with the higher melting point is subsequently chemically dissolved.
It is also possible to inject a plastic with an expanding agent, similar to the process in the production of sponges. Due to the expanding agent, hollow spaces occur, whereby open pores can be created after a short dissolving phase or by another method. Thus an airflow is also generated in this case.
As an overall very wide air stream cross section is possible with a porosity, despite extremely fine individual air entry cross sections, a very homogenous air stream is generated. As the open pores which occur in the case of a woven belt are avoided, the risk of a reduction in porosity occurring during operating time is significantly reduced.
It has been shown that it is very favorable when the transport belt is only a few tenths of a millimeter thick, preferably less than 0.5 mm. The fiber strand to be condensed thus lies almost directly on the suction slit, which results in a good condensing effect.
It is sufficient when the porous area is only located there where the suction slit has to be covered over. A border zone can thus be provided on both sides of the porous area, which zones are not porous and which permit the drive by means of a friction roller or the like.
As a plurality of spinning points are arranged closely adjacent to one another in a spinning machine, it is in certain circumstances purposeful when the transport belt extends over a plurality of spinning stations. It can then be provided that a relatively narrow porous area is arranged to each spinning station.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.